Method of producing phosphoric acid and hydrogen



April 29, '1930. LARSSON 1,756,429

uE'nHoD oF PRoDUcING PHosPHoRIcVAcID ,AND HYDROGEN Fild Maron s1, 19215 l@ 05M, Coo/erY Je/oarazor.

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Patented Apr. `29, 1930 uNiTED STATES PATENT Price MARKUS LABSSON, OF NIAGARA FALLS, NEW YORK, ASSIGNOR, BY

MENTS, TO DU PONT AMMONIA CORYORATION, OF WILMINGTON,

CORPORATION OF DELAWARE METHOD OF MESNE ASSIGN- DELAWARE, A

PRODUICING PHOSPHORIC ACID ANI) HYDROGEN Application filed March 31, 1925, Serial No. 19,581, and in Sweden April 15, 1924.

It has already been proposed to produce phosphoric acid through reduction of water by means of elementary phosphorus at a high temperature so that the phosphorus is oxidized to phosphoric acid by the oxygen of the water, setting the hydrogen free. Aft-er the hydrogen has been separated from the phosphoric acid it is obtained in a practieally pure forni. In order to facilitate the reaction between water and phosphorus so that it can take place at a lower temperature and with greater velocity than otherwise and avoiding the formation of pliosphine, it has been proposed to use certain metals or their oxides as catalyzers. Generally this reaction is carried out by the use of gaseous phosphorus, which is obtained by reducing phosphatic material by carbon in an electric reduction furnace.

The aim of the present invention is also to produce but in a different way phosphoric acid from phosphorus and water obtaining at the same time free hydrogen as a by-product. The present invention consists chieliy in that a phosphide of a metal reducible by hydrogen is brought to react with water or water vapor at a high temperature. rThe metallic phosphide can be produced by reducing phosphatic material by carbon in an electric or other suitable reduction furnace adding the metal or oxides of same so that the inetallic phosphide is obtained as a molten fluid which is tapped off from the furnace and then brought to react with superheated in a Bessemer converter; or the phosphide can also be produced by bringing the gaseous mixture of carbon monoxide and phosphorus obtained by the reduction of phosphatic material in contact with the metal in question at the proper temperature so that the phosphorus is absorbed during the formation of metallic phosphide, which afterwards is reacted upon by means of superheated steam. During the reaction between the metallic phosphide and the steam, the phosphorus of the phosphide is oxidized by means of the oxygen of the steam principally to phosphorus pentoxide at the same time setting hydrogen free. The metal combined with the phosphorus is also s`et free ryin or changed into oxide, while at the same time a corresponding quantity ofhydrogen gas is set free. The metal or oxide can again be used either as an addition in the reductionk furnace or for absorption of a new quantity of phosphorus, in which latter case the metal first iiiust be reduced, if it was changed into oxide at the treatment of the phosphide with steam. ln that way the process can be carried on without any essential loss of metal.

It is not necessary for the conversion of metallic pliosphide into phosphorus pentoxide to use exclusively the oxygen of the Wan ter. The invention alsocovers the ease in which part of the oxygen required is added in the form of free oxygen. In this case steam and air may either be mixed in advance. iii' the desired proportions,

brought together With the .metallic phos and then air or vice versa. This modilication of the invention may be used either when it is desired to obtain hydrogen gas mixe with a certain percentage of nitrogen, or when required for maintaining the desired reaction temperature.

The carbon monoxide formed by the reduction of the phosphatic material can be used for heating the charge for the production of Water vapor and the superheating of saine, etc.

The metals that may be used in the present invention are, of the eighth group of the periodic system, Fe, Ni, and Co, of the seventh group Mii, of the sixth group Cr, Mo, and W, and of the first group Cu. are, however, mainly of theoretical interest.

In Figs. l-B of the attached drawing a before being Several of these for performing three different ways of carg out the invention.

In Fig. 1, A indicates an electric reduction furnace which is charged with phosphate rock, carbon, silica and a metal, or a metal oxide, which is reducible by means of hydrogen, for instance, copper in metallic form or an oxidized copper ore. The phosphorus roduced from the phosphate rock combines with the metal present into metallic phosphide, which gathers in melted form at vthe bottom of the furnace under the melted slag formed simultaneously which slag consists mainly of calcium silicate. AThe furnace A is provided with electrodes B, slag removing holes C, gas outlet D and a tube E through which the phosphide produced 1n the furnace may be drawn olf periodically into a Bessemer converter F. After the converter has been filled to the required height with melted metallic phosphide, steam or steam mixed with a small quantity of air is blown into samethrough a tube C whereby. the phosphorus in the metallic phosphide 1s oxidized into phosphorus pentoxide, which volatilizes at the same time as the metal is reduced and the steam decomposed, so that free hydrogen is obtained. The temperature in the converter should be kept so high that the reduced metal will be kept in a liquid condition and so that, at theend of the reaction, it can be drawn off through the tube N. This regulation of the temperature can be accomplished by regulating the temperature of the l 400 centigrade.

steam and also by regulating the quantity of air added.' The phosphorus pentoxide and hydrogen formed go through a tube I-I into a cooler or boiler K and from there vinto a separating system L where the phosphorus entoxide is separated in some known way, or instance, by electric precipitation or through absorption in water. The hydrogen gas which remains after the separation of the phosphoric anhydride is obtained in1 a pure form, and can,-if mixed with the proper quantity of nitrogen,l be directly utilized for the synthetic production of ammonia.

In carrying out the method shown in Fig. 2 the electric reduction furnace A is charged with phosphate rock, silica and carbon without the addition of any metal or metallic oxide, so that there only takes place a reduction of the phosphate rock which produces a gaseous mixture of elementary phosphorus and carbon monoxide, which mixture is passed through a tube D into a chamber F1, filled with pieces of a metal, for instance, copper which is kept at a temperature exceeding In this chamber the phosphorus is absorbed by the metal forming a metallic phosphide, while the remaining earbon monoxide escapes through a tube M and is then used for the production of steam, for heating the charge, etc. When the copper in the chamber F1 has absorbed the proper uantity of phosphorus, the flow of gas is c anged to flow from the furnace through another absorption chamber F2 and properly superheated water vapor is brought into the chamber F1 through the tube G. In this way the metallic phosphide is reduced to metal at the same time as the water vapor is decomposed. The gaseous reaction products formed consisting of phosphorus pentoxide and hydrogen gas are conducted through the tube H into the cooler or boiler K and the separation system L where the phosphorus pentoxide is condensed well known way. By utilizing alternately in the manner described both of the chambers F1 and F2 for the absorption of the phosphorus by means of a metal in solid forni and the reduction of the metallic phosphide by means of water vapor, the process may be carried on continuously. f

In the method shown in Fig. 3 the electric furnace A is used as shown in Fig. 2 for the reduction of phosphatic rock and the absorption of the gaseous phosphorus coming from the reduction furnace takes place in a chamber F3, containing melted metal, such as for instance, melted copper. Through a partition O, pai-tof which depends from the roof of the chamber into the melted metal, the gas room of the chamber is divided in two parts, g1 and g2, which are not connected with each other. A fan or some other suitable device such as d disposed in the conduit D serves to force the gases coming fromthe furnace A in a finely divided form under the surface of the metal in the part g1 in order that an effective absorption shall take place. The carbon monoxide leaves part q1 through the tube M and is utilized in a suitable way. lV-hen the gases pass the molten metal bath they produce a movement in same so that the phosphide formed is partly transferred to the other part of the chamber (g2). Into this superheated steam is blown through the tube G by which the metallic phosphide is reduced to metal, which through circulation is carried back to part g1 where it absorbs new and separated in the y quantities of`phosphorus while the separated l directly in the reduction furnace it is of course not necessary to treat it immediately after it has the reduction furnace. of advantage to first let it cool oill and solidify, granulate it and afterwards treat by means of steam. When the metallic phos phide is produced outside the reduction furnace by reacting upon a metal by means of the gas coming from a furnace for the reduction of phosphate rock the hydrogen phosphidc in the gas also becomes decomposed by the metal. l

What I claim is p l. The method of producing phosphoric acid and hydrogen gas which comprises reacting upon a phosphide of a metal reducible by hydrogen by means of hydrogen monoxide to oxidize the phosphorus of the phosphide substantially into phosphorus pentoX- by means ofsteam been drawn off from It sometimes may be ide and to set free the hydrogen of the hydrogen-monoxide.

2. The invention set forth in claim 1 in which free oxygen is added to the, hydrogen 5 monoxide.

3. The method of producing phosphoric acid and hydrogen gas which comprises forming a gas mixture from phosphatic material in a reduction furnace, bringing the gas mixture into contact with a metal reducible by hydrogen to absorb the phosphorus and forming metallic phosphide, and then reacting upon the phosphide with hydrogen monoxide at high temperature to obtain phosphorus pentoxide and hydrogen.

4. The invention set forth in claim 3 in which free oxygen is added to the hydrogen monoxide.

5. The method as set forth in claim l characterized in that the metal used is a non-alkali metal of the first group of the periodic system.

In testimony whereof I hereto affix my signature. z5 MARKUSA LARSSON. 

